1. Field
The following description relates to lamp assemblies. In a particular form the following description relates to lamp assemblies for an exterior rear view mirror assembly of a vehicle.
2. Description of Related Art
Automotive lighting arrangements are increasingly being used in vehicle side mirrors (exterior rear view mirror assemblies) as value added features required by automotive manufacturers. An example of this is mirror assemblies that are manufactured with turn signal indicator (STI) lights. Light emitting diodes (LEDs) are also being used more frequently as the light source in these lighting arrangements. In addition to the functionality of these lighting systems, another important design consideration is the aesthetic appearance of the light output from these systems.
In particular, it is desirable to provide a lighting arrangement using one or more LED light sources that is able to provide an output having an even (uniform or homogenous) area luminance). This is difficult to achieve as an LED light source is inherently directional (with an approximate Lambertian distribution) meaning that the relative luminous intensity of the LED varies away from the central axis of the LED. The luminous intensity is highest at 0° (along central axis) and drops off significantly as the viewing angle approaches 90°. Because of this, a lighting arrangement using a series of LED light sources tends to create a series of “hot spots” (or conversely dark regions) that are visible to an external viewer of the lighting arrangement. In other words, the light output is not of even intensity across a particular viewing surface.
One method of obtaining a light output over a surface having substantially uniform luminous intensity using one or more LED light sources is to use a dedicated light pipe that receives light from the LED light source(s) and directs it towards a targeted output surface (usually by using a range of optical surfaces-surface defects, etches, shaped optics etc). While a light pipe could be used, this solution may not be cost feasible due to the cost associated in manufacturing the light pipe.
There is therefore a need to provide a useful alternative to using a light pipe in a lighting arrangement that provides a light output over a surface having substantially uniform luminous intensity using one or more LED light sources.
Other advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, a preferred embodiment of the present invention is disclosed.